Air line branch. Scheme, description

ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Air line branch. Encyclopedia of radio electronics and electrical engineering

Free technical library

Encyclopedia of radio electronics and electrical engineering / Electric installation work

Branch perform without installing additional supports, if its length from the overhead line is not more than 25 m. It is recommended to use insulated wires for a branch, but uninsulated wires are also allowed; in this case, a soft insulating tube can be put on each wire.

If the branch length exceeds 25 m, it is necessary to install additional supports. From the overhead line to the last support, an uninsulated wire is mounted, and from the last support to the building - insulated.

The smallest allowable cross-section (mm) of wires for branches to individual consumers, according to the conditions of mechanical strength, is:

Overhead line branch

It is more convenient to carry out a three-phase (four-wire) branch with a four-wire wire of the AVTV or AVTU brand with a built-in carrier cable, the cross section of aluminum current-carrying wires can be at least 4 mm, since it is not they that perceive the mechanical load, but the cable.

The carrier cable is tightly fixed and attached (Fig. 8) to the neutral wire. An additional insulator is placed on the support to attach the cable.

Overhead line branch
Rice. 8. Branch from the overhead line with a wire with a carrier cable: 1 - additional insulator; 2 - cable; 3 - branch wires; 4 - zeroing of the cable; 5 - zero core; 6 - insulator for outdoor lighting wire

Insulators are also installed on the wall of the building. For AVTV, AVTU wires, one insulator is needed, on which the carrier cable is fixed, in other cases - according to the number of wires: two insulators for single-phase input or four for three-phase. Porcelain or glass insulators of types TF-12, TF-16, RFO-12 or NS-16 are used.

The distance from the branch wires to the ground when crossing the carriageway must be at least 6 m, when crossing the footpath - at least 3,5 and at the insulators on the wall - at least 2,75 m (Fig. 9).

Overhead line branch
Rice. 9. Normalized branch distances from overhead lines: 1 - carriageway; 2 - footpath; 3 - VL support; 4 - additional support Insulators can be installed side by side or one below the other. The distance from the wires to the ground surface must be at least 2,75 m, and between the wires and from the wires to the protruding parts of the building (roof, gutter, etc.) - not less than 0,2 m.

Overhead line branch
Rice. 10. Mounting the bushing insulator on wooden and stone walls

The insulators are first fixed on hooks, then the hooks are mounted on the outer wall (Fig. 10). In buildings with concrete or brick walls, a nest is punched for each hook to a depth of 100 mm and the hook is fixed with cement mortar. In buildings with chopped walls, holes are drilled for mounting hooks and hooks are screwed into them. In frame-backfill, adobe or plank structures, hooks are installed on a wooden beam 70-100 mm thick, which is mounted on the wall with screws or studs. Sometimes from the inside it is required to strengthen the wall with a board, and attach a beam to it through a thin wall of the building.

For a branch, you can use a cable with copper conductors (VVG, PVG, etc.) with a cross section of at least 22 mm or aluminum conductors (AVVG, APVG) with a cross section of at least 2,5 mm.

The cable is laid along the support post: in the upper part it is open on brackets, and from a height of at least 1,5 m from ground level - in a pipe to a depth of 0,7 m. Then the cable is led in a trench with a depth of at least 0,7 m to the building and , finally, in the pipe they lead to the outer wall. In the trench, the cable is laid on a layer of earth that does not contain stones, slag and construction debris. Above the cable perform the same backfill. In places where excavation is likely, concrete tiles or bricks are laid on top of the backfill layer.

Overhead line branch
Rice. 11. Entering the building through pipe racks: a- through the roof; b - through the wall

The branch is considered part of the overhead line, it is served by the owner of the electrical networks to the insulators on the wall of the building, including the connections at the insulators.

With a cable branch, the owner of the network maintains the cable and the contact connections of its lugs.

Author: Bannikov E.A.

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